That's a convenient dodge...
Why is it not just as equally unreasonable to question why the Universe needs a cause? If you can exempt god from your rule, then your rule is bogus.
Watch this:
It's an unreasonable question to ask who created the creator. Who says she was created in the first place?! We as human are limited in our understanding of the whole picture. Humans have this uncanny ability to fabricate whatever it is they want into things that are unknown. There is no answer as to who created the creator other than the classical view that she always existed. I am speaking, of course, about our mother goddess, Nana Buluku.
Does your exact same argument for Yahweh work when I make it for Nana Buluku? If it does not, then you have a serious problem. If it does, then you have a serious problem...
https://en.wikipedia.org/wiki/Nana_Buluku
But I digress...
Beneficial mutations (or neutral) are the only ones that are going to be kept in populations over long periods of time. What survives is what ends up being passed on - anything that hinders survival is going to be less prominent in future generations. So, only the good stuff gets kept. Bad stuff is weeded out. It's simple. (as a ridiculous example, one-legged humans aren't going to outrun many predators. They would get picked off first, leaving only the two-legged humans to mature into adulthood and produce offspring. The one-legged human "mutation", and perhaps the clunky three-legged human, would not make it very far in the legged human timeline, leaving only the more successful two-legged human.)